1. Field of the Invention
The present invention relates to a drive apparatus for a magnetic head used in an optomagnetic recording system and, more particularly, to a drive circuit apparatus for a magnetic head used in information recording of a magnetic field modulation scheme.
2. Related Background Art
In recent years, an optomagnetic recording apparatus has received a great deal of attention as a large-capacity external memory for a computer. An optical modulation scheme and a magnetic field modulation scheme are available as existing information recording schemes for the optomagnetic recording apparatus. Of these modulation schemes, the magnetic field modulation scheme has an advantage in that information recording can be performed without decreasing information transfer speed since an overwrite operation can be performed to simultaneously erase recorded information and write new information.
FIG. 1 is a schematic circuit diagram for driving a magnetic head used in the above magnetic field modulation scheme. In the magnetic field modulation scheme, as is known well, a light beam is emitted from a light source such as a semiconductor laser to an information recording medium to increase the temperature of an irradiated portion over a Curie point, and a magnetic field modulated in accordance with a recording signal is applied to this high-temperature portion, thereby changing the direction of magnetization in correspondence with the bit information. The circuit shown in FIG. 1 is an arrangement of a magnetic head using two coils L.sub.1 and L.sub.2 to generate a bias magnetic field. A switch element SW1 is connected to the coil L.sub.1 through a resistor R.sub.1, and a switch element SW2 is connected to the coil L.sub.2 through a resistor R.sub.2. A recording signal is supplied to the control terminal of the switch element SW1, and to the control terminal of the switch element SW2 through an inverter 100. As shown in FIG. 2, the coils L.sub.1 and L.sub.2 are wound around a magnetic core 101 serving as a magnetic field generation core in opposite directions. Terminals a to d of the coils in FIG. 2 correspond to those in FIG. 1. When a current is supplied from the terminal a to the terminal b, the coil L.sub.1 generates a magnetic field having a given direction of polarization. When a current is supplied from the terminal c to the terminal d, the coil L.sub.2 generates a magnetic field having a direction of polarization opposite to the given direction.
Assume that the recording signal is set at "1". Since the switch element SW1 is turned on and a current flows through the coil L.sub.1, a magnetic field is generated by the coil L.sub.1. At this time, since the switch element SW2 is kept off, no magnetic field is generated by the coil L.sub.2. On the other hand, when the recording signal is set at "0", the switch element SW1 is kept off, and the switch element SW2 is turned on. Therefore, a magnetic field is generated by the coil L.sub.2. The direction of the magnetic field generated by the coil L.sub.1 is opposite to that of the magnetic field generated by the coil L.sub.2. Therefore, bias magnetic fields having different polarities corresponding to the levels of the recording signals can be generated.
FIG. 3 shows a magnetic head for generating a bias magnetic field by using one coil. In this arrangement, a current is switched and selectively supplied to a coil L.sub.3 by using four switch elements SW1 to SW4. The recording signal is directly input to the control terminals of the switch elements SW2 and SW3, and to the switch elements SW1 and SW4 through an inverter 102. The coil L.sub.3 is wound around a magnetic core 103, as shown in FIG. 4. By changing a current flow direction, the polarity of the generated magnetic field is changed. Terminals e and f of the coil shown in FIG. 4 correspond to those in FIG. 3.
In the above arrangement, for example, when the recording signal is set at "1", the switch elements SW2 and SW3 are turned on, and a current is supplied to the coil L.sub.3 in a direction extending from the terminal f to the terminal e. On the other hand, when the recording signal is set at "0", the switch elements SW1 and SW4 are turned on, and a current is supplied to the coil L.sub.3 in a direction from the terminal e to the terminal f. The direction of the magnetic field generated by the coil L.sub.3 is changed, and therefore a bias magnetic field corresponding to the level of the recording signal can be generated.
In the magnetic field modulation scheme, the magnetic head is not used to reproduce information. It is, therefore, possible to maximize the distance between a recording medium and the magnetic head. An accident such as a head crash can be prevented. A magnetic field generated by the magnetic head must be larger than that generated by a magnetic recording apparatus such as an HDD. For this purpose, the coil must have a large inductance, and a current flowing through the coil must also be large. In order to always obtain a high-quality reproduced signal, a time (to be referred to as a switching time) required for reversing the magnetic field must be minimized.
In the conventional example described above, in order to satisfy this requirement, a power source voltage applied to the coil must be high. For this purpose, a new power source for the magnetic head is required in an optomagnetic recording apparatus, thus complicating the arrangement of the apparatus and increasing the size and cost of the apparatus.